I think you mean ASM - Automatic Storage Management, not ASSM - Automatic
Segment Space Management. ASM is the one with a different instance to manage
physical storage of data. If you do mean this then yes we are using it in
RAC environment (10gSE so its mandated). Seems to work reasonably well so
far.

Not the
> tablespace level stuff, but the create a mount point & let Oracle decide> the file names, etc...

technically wouldn't that be Oracle Managed Files or OMF? You can do this on
a plain file system quite simply since (IIRC 9i Release 1).

I'm interested in knowing if your using it with
> a single instance database or a RAC system or both.